1. Technical Field
The present invention relates to a driving device of an electrophoretic display (EPD) and an improved driving method thereof.
2. Related Art
An electrophoretic apparatus includes an electrophoretic display panel in which display corresponding to a plurality of divided electrodes (segment electrodes) driven by moving electrophoretic particles, which are contained in insulating liquid existing between a transparent common electrode and the divided electrodes disposed opposite to the common electrode, by application of a voltage between the common electrode and the divided electrodes is performed. Furthermore, in order to operate the electrophoretic display panel, the electrophoretic apparatus includes a driving device that drives the common electrode and each of the segment electrodes in correspondence with information to be displayed. The driving device includes a data holding circuit, which holds a plurality of information items used to set voltages of the common electrode and the segment electrodes, and a driving circuit that drives the common electrode and the segment electrodes in correspondence with the information held in the data holding circuit.
In the electrophoretic apparatus, colored electrophoretic particles move to either a common electrode or segment electrodes, thereby performing display. Accordingly, it generally takes a time until the movement of the electrophoretic particles is completed after a voltage is applied to the segment electrodes. For this reason, since the responsiveness is not good, the electrophoretic apparatus is mainly used for display of a still image. A variety of improvements has been suggested to improve the responsiveness.
For example, JP-A-52-70791 discloses an example in which a study on control of application of a voltage to a common electrode and each segment electrode is made to shorten the response (movement) time of electrophoretic particles in an electrophoretic display that uses a common electrode and a plurality of segment electrodes used to display a character, a numeral, a symbol, or a picture.
As mentioned above, in order to drive an electrophoretic display panel, voltage data applied to the common electrode and each segment electrode should be supplied as display data to the data holding circuit for the common electrode and each segment electrode. For example, the display data is supplied from an external computer to a serial input interface of a driving device. In the case of performing serial transmission of display data to a driving device, in order to change a voltage level of either a common electrode or a plurality of segment electrodes, all data of the common electrode and the segment electrodes should be transmitted to update all data held in a display information holding circuit.
However, as will be described later, the inventor has found out that the movement of electrophoretic particles, of which positions are to be changed, can be promoted by inverting only a voltage level of a common electrode at proper periods without changing a voltage of each segment electrode.
Even in the case of performing control in such an operation state, in the driving device described above, the entire display data of the common electrode and all segment electrodes should be supplied whenever the voltage level of the common electrode is inverted.
Accordingly, even in the data transmission side (external computer side) as well as the driving circuit of the electrophoretic display panel, burden of data processing for forming serial data and useless power consumption due to the data processing prohibit the entire system including the electrophoretic display panel from operating with low power. Furthermore, since processing at the transmission side becomes complicated, it is necessary to make a circuit operate at high speed, for example, by increasing the number of operating clock cycles of a computer, which is disadvantageous in terms of cost.